The invention relates to a method for capping an electric lamp in accordance with the preamble of Patent Claim 1.
Such a method for capping an electric lamp is disclosed, for example, in European patent specification EP 0 455 884 B1. This patent specification describes the capping of a high-pressure discharge lamp capped at one end, in the case of which a tubular extension of the discharge vessel is sealed in a thermoplastic synthetic cap part with the aid of a means capable of high-frequency-induced heating.
It is the object of the invention to specify a method for capping an electric lamp, which method is simplified by comparison with the prior art.
This object is achieved according to the invention by means of the characterizing features of Patent Claim 1. Particularly advantageous designs of the invention are described in the subclaims.
The capping method according to the invention can be applied to electric lamps which have a lamp cap provided with a thermoplastic synthetic cap part, and at least one lamp vessel which is connected to the thermoplastic synthetic cap part by a fused bond. According to the invention, this fused bond is produced by heating sections or parts of the at least one lamp vessel to a point which is greater than or equal to the softening point and, advantageously, greater than or equal to the melting point, of the thermoplastic synthetic cap part material, and by inserting the heated lamp vessel sections into at least one holder of the synthetic cap part, the dimensions of which holder are smaller than the corresponding external dimensions of the lamp vessel sections to be fastened in the holder. When the heated lamp vessel sections are being inserted into the at least one holder, the synthetic cap part material is softened or melts by contact with the heated lamp vessel sections, and the softened plastic or the polymer melt is displaced by the penetrating lamp vessel sections. In this way, the initially too narrow holder is widened and matched to the external dimensions of the lamp vessel sections penetrating into it. After the softened plastic or polymer melt has been allow to set, the at least one lamp vessel is surrounded in a self-closed fashion by the set synthetic material. The set synthetic material advantageously forms a ring-shaped collar surrounding the at least one lamp vessel in a self-closed fashion. The ring-shaped collar enlarges the contact area between the at least one lamp vessel and the synthetic cap part and thereby increases the stability of the fused bond. In order for the production of the fused bond according to the invention to use up as little time as possible, the lamp vessel sections are preferably heated to a point which is even substantially above the melting point of the thermoplastic synthetic cap part material, but also substantially below the melting point of the discharge vessel.
In order to reduce the risk of the occurrence of cracks in the at least one lamp vessel during the sealing method according to the invention, before the heated lamp vessel sections are inserted into the at least one holder, the synthetic cap part is advantageously preheated to a point which is above room temperature and below the softening point of the synthetic cap part material. It is advantageous to accelerate the setting of the plastic by cooling the sealing region, preferably by means of an airflow. In order to increase the strength of the fused bond, the at least one lamp vessel is advantageously provided with at least one indentation, and the heated lamp vessel sections are inserted into the at least one holder in such a way that the at least one indentation is embedded in the set synthetic material in a self-closed fashion after the setting of the plastic. The at least one holder is advantageously designed as a depression or cutout in the thermoplastic synthetic cap material, and the at least one lamp vessel is of U-shaped design, the limbs of the at least one U-shaped lamp vessel being sealed in a depression or a cutout in the synthetic cap part.
The capping method according to the invention can be applied with particular advantage in the case of fluorescent lamps which have a synthetic cap and a discharge vessel which comprises at least one U-shaped glass tube. Usually, with such fluorescent lamps, which are frequently also denoted as compact fluorescent lamps, the discharge vessel is fixed by means of a cement ring in a depression or a cutout in a cap-type synthetic cap part. Such a lamp is described, for example, in patent specification EP 0 452 743 B1. The application of the capping method according to the invention to the aforementioned fluorescent lamps permits cement to be dispensed with. The fluorescent lamp according to the invention is therefore distinguished by a lamp cap which has at least one thermoplastic synthetic cap part which has a permanent fused bond with the limbs of at least one U-shaped glass tube which is a constituent of the discharge vessel of the lamp. The at least one thermoplastic synthetic cap part is advantageously designed as a cap through which the limbs of the at least one U-shaped glass tube are led, and which has on the inside ring-shaped collars which surround the limbs of the at least one U-shaped glass tube in a self-closed fashion. The cap advantageously closes off a lamp cap which is of pot-type design and in which a ballast is arranged for operating the fluorescent lamp.